WASHINGTON
— The failure of a major federal prosecution of a suspected terrorist supporter is drawing two radically different reactions.

Many Muslim-Americans are hailing the acquittal of former college professor and Palestinian activist Sami al-Arian as a vindication of the US system of justice. But others see the outcome of the five-month federal trial in Tampa as a setback to US government efforts to halt the flow of money and other support to illicit Islamic and Arab causes in the Middle East.

The trial of Mr. Arian was billed as a showcase of how beefed-up investigative powers authorized under the Patriot Act were helping protect the nation from a repeat of the 9/11 attacks. But on Tuesday, a federal jury in Tampa acquitted him on some terror support and murder conspiracy charges and deadlocked on others.

Arian's acquittal comes two weeks after the government announced its intention to move suspected terrorist Jose Padilla from military custody in South Carolina to a Miami federal lockup. The government is seeking to put Mr. Padilla on trial - not on its original allegations that he was planning to build a radiological or so-called "dirty" bomb but rather on charges that he associated with others in Florida who allegedly supported militant Muslim causes.

The approach is similar to the al-Arian prosecution that relied heavily on his association and communications with suspected terrorists in the Middle East. Critics see a government attempt to prove guilt by association. Other analysts stress the difficulty of building a criminal case against shadowy groups organized in secret cells.

At the time of Arian's indictment in 2003, John Ashcroft, then US attorney general, said the outspoken activist was in fact the US leader of Palestinian Islamic Jihad. The group, responsible for hundreds of deaths in suicide bombings in Israel, was designated a terrorist organization by the State Department in 1995.

Arian's lawyers admitted during the trial that their client communicated with top members of the PIJ and that he cheered whenever he heard that the group had launched another deadly suicide attack in Israel. But the contacts came before 1995, when the government made material support of the PIJ a crime.

Defense lawyers said al-Arian was a member of the political wing of the PIJ rather than the group's violent military wing. They said his fundraising was oriented toward legitimate charity for needy Palestinians, not to help perpetuate the cycle of violence in the Middle East.

After 13 days of deliberations, the jury in Arian's trial found him not guilty of eight of the 17 charges in his indictment. He was cleared of charges that he conspired to murder and maim individuals in Israel, and that he had provided material support to a terror group.

Federal prosecutors are considering whether to retry Arian on the hung-jury counts.

Several jurors have been quoted in the media as saying that the government failed to present enough evidence to support the charges.

To build their case, prosecutors presented 70 witnesses and thousands of hours of wiretapped telephone conversations. The evidence, covering some 400,000 intercepted calls, was gathered during nine years of surveillance of Arian by US intelligence agents.

The most significant break in the investigation came following the 9/11 terror attacks when Congress passed the Patriot Act.

The new law dismantled a wall that had been erected between foreign counterintelligence agents spying on individuals in the US and federal prosecutors. Prior to the Patriot Act, evidence discovered during such domestic surveillance operations could not be used in a criminal prosecution. The new law changed that.

The trial itself revolved around a more fundamental issue. Defense lawyers argued that the case against Arian was political, that he was being punished for having a different - and unpopular - perspective on the Palestinian-Israeli conflict.

Many Arabs and Muslims in the US were closely monitoring the Arian case but were fearful to speak out about what they saw as an effort to paint Arian as a terrorist because of his religious and political beliefs.

To them, the jury verdict was a welcome surprise.

"This restores our faith in the American justice system," says Ahmad Bedier, Florida representative of the Council on American-Islamic Relations. "It sends an important message that in post 9/11 America, Muslims can get a fair trial."